This invention is directed to hollow core panels and, in particular, truss core panels.
Various types of hollow core panels have been proposed by the prior art. While there may be exceptions, hollow core panels generally fall into one of two general groups--honeycomb core panels and truss core panels. Often, the terms "honeycomb core" and "truss core" have been confused. As used herein, honeycomb core panels are panels having a core structure formed of a multiplicity of adjacent cells, the walls of which intersect the face sheets of the panels, usually at right angles. Contrariwise, truss core panels are panels formed of a plurality of elongate core elements arrayed such that their longitudinal axes lie parallel to one another and parallel to the face sheets of the panels. The present invention is directed to truss core panels as thus defined.
Many prior art truss core panels include core elements that have a circular cross-sectional shape. The primary disadvantage of truss core panels that include such core elements is that their resistance to shear loads orthogonal to the longitudinal axis of the core elements is not as great as truss core panels that include core elements having other cross-sectional configurations, such as panels that include core elements having a rectangular cross-sectional configuration. On the other hand, circular core elements are relatively easy to assemble because they readily self-align with one another (and the enclosing face sheets) at tangent points, after they have been roughly arrayed in side-by-side positions; whereas, rectangular core elements must be individually positioned.
Thus, while core elements having a rectangular cross-sectional configuration are substantially stronger in shear than core elements having a circular cross-sectional configuration, rectangular core elements have assembly disadvantages. More specifically, rectangular (including square) core tubes cannot be merely roughly arrayed on a suitable face sheet and gently vibrated into position, as can be done with circular cross-sectional tubes. Rather, rectangular tubes must be individually positioned, which is a time-consuming manufacturing operation. Therefore, panels that include core elements having a rectangular cross-sectional shape are expensive to manufacture.
While proposals have been made to use core elements having cross-sectional configurations other than circular or rectangular, panels using such core elements have other disadvantages. For example, panels having corrugated core elements have been proposed. Corrugated core panels have the disadvantage that they are not as strong (for the same wall thickness) as either circular or rectangular core element panels. In addition, proposals have been made to use discontinuous triangular shaped core elements. One example of a panel including discontinuous triangular shaped core elements is described in U.S. Pat. No. 4,001,474 entitled "Honeycomb Panel Cellular Structure Having Triangular Cells" by Ralph F. Hereth. The problem with such panels is that the triangular shaped core elements are discontinuous or "broken" at one apex and, thus, not as strong as continuous elements. Further, the core elements described in this patent must be individually arrayed.
Therefore, it is an object of this invention to provide new and improved truss core panels.
It is a further object of this invention to provide truss core panels that are easy to assemble.
It is another object of this invention to provide truss core panels that are easy to assemble yet have orthogonal, longitudinal shear strength greater than the shear strength provided by truss core panels that include core elements having a circular cross-sectional shape, for the same wall thicknesses core elements.
In the past, both the core elements and the face sheets of high shear strength truss core panels usually have been formed of homogeneous materials such as metals or metal alloys. In recent years, various materials having high strength-to-weight ratios, such as glass and graphite fiber materials have been developed. Because of their strength-to-weight advantages, the use of these composite materials in many environments is desirable. In particular, panels formed of these materials are desirable in environments where strength-to-weight ratios are a significant factor. For example, strength-to-weight ratios are a significant factor in the choice of aircraft components because it is desirable to provide maximum strength for the least weight in order to economize on fuel.
Therefore, it is another object of this invention to provide truss core panels formed of a composite, rather than a homogeneous, material.
It is another object of this invention to provide truss core panels wherein the face sheets and/or core elements are formed of a composite material.